Typical digital communication systems involve using a transmitter to send a bit stream to a receiver. The bit stream contains digital information that the receiver decodes and makes use of. In some communications systems, the digital information is extracted by first converting the analog representation of the bit stream to digital samples. Each sample represents the signal at the time of sampling. Because of noise and other effects, signal transitions may not be cleanly represented.
Such digital communication can be used in different systems, such as a Global Navigation Satellite System (GNSS). GNSS is a satellite system that involves a network of satellites in space. Each satellite wirelessly transmits coded signals at precise intervals. A receiver analyzes the signal information to determine position, velocity, and time estimates. The GNSS signal is used for various applications such as to determine the geographic location of a user's receiver anywhere in the world. Using the information in the transmitted signal, the receiver on or near the earth's surface can calculate the exact position of the transmitting satellite and the distance (from the transmission time delay) between the satellite and the receiver. For accurate operation of a system based on receipt of GNSS signals, the transmitting satellite and the receiver are time synchronized.
GNSS are especially sensitive because the GNSS signals are communicated between satellites above the earth's atmosphere and receivers on the earth's surface. In addition, the signals transmitted to the receiver are generated by the transmitter and therefore synchronized to the time base in the transmitter. Thus, the signals are not synchronized to the receiver's time base, and therefore the location of bit transitions in the receiver's time base cannot be assumed.